Hi, Terry,
Short answer: Mostly people never try double FCP's because they don't have
the room. In addition, something we can't model, there are technical
suspicions why double wire may not give you double performance. Anybody on
the reflector that actually has done double FCP's we'd love to hear.
Long Answer:
I have modeled dual FCP's very early on, but I have never trusted the
ground loss calculations from NEC4.
We have not put up crossed FCP's at K2AV. Impinging trees trying to place
crossed FCP's would probably require cutting down trees to make space and
create the 5 foot separation around the wires. That isn't going to happen.
There is a reason my wife and I bought woodsy property to retire. We remove
rotted, clearly failing trees, and we cut down sweet gum trees, or those
threatening the house. The wife sometimes complains about diminished
sunlight for plants, but won't go for cutting down trees to get more
sunlight.
Deploying an SAL-30 RX antenna has a similar problem with threading trees,
but I will figure out a way to get a good RX antenna on property.
I have had a half-dozen, maybe dozen inquiries, on the crossed FCP's
question over five years. In contrast, we have many, undiminishing requests
centering on how to match a now efficient inverted L over FCP to 50 ohm
coax. These requests number in the hundreds. We have spent the bulk of time
with the bulk of our inquiries, guided where to spend our time by the bulk.
These tendencies are confirmed in which pages on the web site are hit the
hardest.
Not to diminish your inquiry in any way, I think there are a number of ways
to explain the relative rarity of your request.
1) A single FCP deployment takes up a 66' line. Two FCP's take up a 47 foot
square from tip to tip to tip to tip. A great many FCP deployed properties
simply have nowhere to put 47' x 47'. Deployment at/near and parallel to
the property line is far and away the most common FCP deployment, with
nothing in second place.
2) Once an FCP is deployed replacing a sparse, irregular, undersized radial
system, the second FCP could not possibly repeat the improvement of the
first FCP. A far more fertile field for additional loss mitigation is the
collection of issues listed in the "Loss List" on k2av.com . 1) + 2),
called an FCP+ project on the web site, can be a startling improvement.
There are two modes of loss in the dirt setting the FCP loss performance.
1) Current in the FCP creates fields, whose net at/in the dirt induces
current in the dirt to the degree permitted by the nature of the dirt.
Doubling the FCP will reduce fields at dirt. However...
2) The other mode of counterpoise loss is simple capacitive coupling to the
infinite ground sink, after the well known pattern of pre-lightning ground
current beneath charged clouds. The point of highest capacitive current to
the ground is from the last 1/16 wave of wire. Doubling the FCP doubles
that lossy current, quadrupling the loss.
This and other non-radial-ish FCP aspects are currently under
experimentation, and given that the Almighty grants me time to get through
it all, we may have some sturdy ways to approximate these issues.
But the major conclusion at this time must be that the second FCP will
never recover the same loss as a careful "Loss List" project from the web
page.
73, Guy K2AV
On Tue, Oct 24, 2017 at 11:32 AM, Terry O <cpa599@gmail.com> wrote:
> Has anyone modeled and or built an L or vertical with multiple FCP's?
>
> Any advantage to this vs single FCP?
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